ELECTRIC-FIELD INDUCED PERCOLATION IN MICROEMULSIONS - SIMULATION OF THE ELECTRIC-CONDUCTIVITY

Structure changes can be induced by high electric fields in microemulsions which bring the system from a nonconducting state to a highly conducting state. We report conductivity and electric birefringence measurements in a microemulsion, stabilized by the nonionic surfactant Igepal CO-520 (10 wt% 0.01 M KCl/40% n-hexane, 40% c-hexane/10% Igepal). Based on the experimental findings we investigate two models which may be relevant for understanding the field induced percolation behavior. Computer simulations of the electric conductivity, using the random walk approach, are performed with the following heterogeneous systems: (a) statistically distributed conducting Ising chains in a nonconducting matrix, (b) nonconducting overlapping spberes in a conducting medium. Both systems are capable of modelling certain aspects of the observed percolation. The continuum percolation with overlapping spheres puts special emphasis on the Bruggeman equation of the conductivity in dispersed systems, which is found to be valid in a much wider range than might have been thought before.